In various countries of the world, attempts have been made to provide a stereoscopic color television transmitting-receiving system. None of them has brought a satisfactory result, however. In order to make a new system compatible with the existing systems such as NTSC, SECAM or PAL system, it is necessary to shut out ordinary light so that a holographic, stereoscopic picture may be taken and then transmitted. For the same purpose it is also necessary to solve many problems, such as protection of the human body against laser beams. All in all, it seems almost impossible at present to make the bandwidth of a required carrier wave fall within the bandwidth of the existing systems.
It is easy to provide a system which uses two cathode ray tubes of the same size for reproducing two pictures in a stereoscopic relation, and two polarized glass filters which are disposed on the screens of the cathode ray tubes and different in phase by 90.degree.. Through the glass filters and through polarized eyeglasses a stereoscopic picture may be seen by both eyes of a viewer. But the receiver is inevitably bulky, and the viewer cannot see a stereoscopic picture unless he wears polarized eyeglasses.
Other two-picture systems, a complementary color picture system and a synchronized liquid crystal eyeglass system, are under development. Either system needs specially designed eyeglasses or a viewing aid. Without wearing the special eyeglasses or using the viewing aid, a viewer cannot see a stereoscopic picture.
An attempt has been made to provide a system which uses a lenticular screen in combination with two stereoscopic pictures so that a viewer may watch a stereoscopic picture without wearing a specially designed viewing aid. (For example, U.S. Pat. No. 3,674,921 discloses such a system.) The system is theoretically unworkable. A viewer can watch a stereoscopic picture only when he stands in front of the screen. If he stands at other positions, he can watch but a flat picture or, in worst case, a pseudoscopic picture in which far and near are replaced with each other. This system is therefore not practical.